This invention relates to a flow quantity measuring apparatus, and more particularly a flow quantity measuring apparatus capable of detecting erroneous operations of a converting circuit in the flow quantity measuring apparatus.
A conventional flow quantity measuring apparatus for such fluids as aqueduct water, town gas, etc., was constructed as shown in FIG. 1, for example. Thus, it comprises a detection circuit 1 including an impeller, not shown, driven by the fluid to be measured for producing pulse signals corresponding to the flow speed of the fluid, a converter 2 which converts the output signal of the detection circuit 1 into a value corresponding to the flow quantity (quantity of consumption) of the fluid, a counter 3 counting the number of the output signals from the converter 2, a display circuit 4 and a display device 5 which displays the content of the counter 3 whereby to detect and display the quantity of water or gas consumed.
In the flow quantity measuring apparatus of the type described above, depending upon the volume and type of the fluid to be measured it is necessary to apply a weight (multiplying factor) to the converter 2. For example, in apparatus for measuring the quantity of aqueduct water, the converter 2 converts each revolution of an impeller in the detecting circuit 1 into the quantity of water in liters and the output of the converter is integrated by the counter 3 to determine the quantity of water used. To add a weight to the converter 2 a read only memory device ROM or wirings and switches on a printed substrate have been used. Where a ROM is used, however, it is not easy to vary the weight, whereas use of switches requires a large space.
As a method of adding a weight without accompanying these difficulties it has been proposed a method according to which a shift register and a counter are incorporated into the converter of the measuring apparatus. According to this method, the detector is constituted by a rate multiplier supplied with the pulse signal from the detection circuit 1 and a register that sets the weight (multiplying factor) of the rate multiplier. By prestoring a suitable value in the register the rate multiplier supplies a signal (number of pulses) corresponding to the measured quantity to the counter 3. With such a converter, when the flow quantity measuring apparatus is miniaturized or fabricated with an integrated circuit, the setting of the weight becomes easy and the number of pins of the integrated circuit can be reduced. However, an integrated circuit memory device, i.e., the register has a defect that its content is varied due to external noise or a momentary interruption of the power supply.